When I had a turkey fryer I boiled slightly less than 1g/hr but I wasn't on propane, I was stove-top so my boil might have been less vigorous.

I'd shoot for 6.5. You'll absorb plenty in the hops and then boil off nearly another gallon. You'll need to be careful though because most of those turkey fryers are 30qt, or 7.5g. I'd gently boil for a while until you can afford to turn it up and not have a boilover. After the initial foam subsides.

Great! Yes, I will be boiling with turkey fryer burner. My last batch was another big beer and I had 17lbs of grain to boil. I did the boil in a bag. I threw in 9 gallons of water into the 15 gallon pot. I ended up with exactly 5 gallons in my ferm bucket. So this time I'm stepping it up by using the mash/sparge technique. I'm getting ready to bottle that one. This one I will keg it. Thanks again!